Photoresist topcoat compositions and methods of processing photoresist compositions

ABSTRACT

Photoresist topcoat compositions, comprising: a first polymer comprising a first repeat unit of general formula (I) and a second repeat unit of general formula (II): 
     
       
         
         
             
             
         
       
     
     wherein: R 1  independently represents H, F or optionally fluorinated C1 to C4 alkyl; R 2  represents optionally fluorinated linear, branched or cyclic C1 to C20 alkyl; L 1  represents a single bond or a multivalent linking group; and n is an integer of from 1 to 5; a second polymer comprising a first repeat unit of general formula (III) and a second repeat unit of general formula (IV): 
     
       
         
         
             
             
         
       
     
     wherein: R 3  independently represents H, F or optionally fluorinated C1 to C4 alkyl; R 4  represents linear, branched or cyclic C1 to C20 alkyl; R 5  represents linear, branched or cyclic C1 to C20 fluoroalkyl; L 2  represents a single bond or a multivalent linking group; and n is an integer of from 1 to 5; and a solvent. Coated substrates coated with the described topcoat compositions and methods of processing a photoresist composition are also provided. The invention finds particular applicability in the manufacture of semiconductor devices.

FIELD OF THE INVENTION

This invention relates to photoresist topcoat compositions that may beapplied above a photoresist composition. The invention finds particularapplicability as a topcoat layer in an immersion lithography process forthe formation of semiconductor devices.

BACKGROUND OF THE INVENTION

Photoresists are used for transferring an image to a substrate. A layerof a photoresist is formed on a substrate and the photoresist layer isthen exposed through a photomask to a source of activating radiation.The photomask has areas that are opaque to the activating radiation andother areas that are transparent to the activating radiation. Exposureto activating radiation provides a photoinduced chemical transformationof the photoresist coating to thereby transfer the pattern of thephotomask to the photoresist-coated substrate. Following exposure, thephotoresist is baked and developed by contact with a developer solutionto provide a relief image that permits selective processing of thesubstrate.

One approach to achieving nanometer (nm)-scale feature sizes insemiconductor devices is to use shorter wavelengths of light. However,the difficulty in finding materials that are transparent below 193 nmhas led to the immersion lithography process to increase the numericalaperture of the lens by use of a liquid to focus more light into thefilm. Immersion lithography employs a relatively high refractive indexfluid, typically water, between the last surface of an imaging device(e.g., KrF or ArF light source) and the first surface on the substrate,for example, a semiconductor wafer.

In immersion lithography, direct contact between the immersion fluid andphotoresist layer can result in leaching of components of thephotoresist into the immersion fluid. This leaching can causecontamination of the optical lens and bring about a change in theeffective refractive index and transmission properties of the immersionfluid. In an effort to ameliorate this problem, use of a topcoat layerover the photoresist layer as a barrier between the immersion fluid andunderlying photoresist layer has been proposed. The use of topcoatlayers in immersion lithography, however, presents various challenges.Topcoat layers can affect, for example, process window, criticaldimension (CD) variation and resist profile depending on characteristicssuch as topcoat refractive index, thickness, acidity, chemicalinteraction with the resist and soaking time. In addition, use of atopcoat layer can negatively impact device yield due, for example, tomicro-bridging defects which prevent proper resist pattern formation.

To improve performance of topcoat materials, the use of self-segregatingtopcoat compositions to form a graded topcoat layer has been proposed,for example, in Self-Segregating Materials for Immersion Lithography,Daniel P. Sanders et al., Advances in Resist Materials and ProcessingTechnology XXV, Proceedings of the SPIE, Vol. 6923, pp.692309-1-692309-12 (2008). A self-segregated topcoat would theoreticallyallow for a tailored material having desired properties at both theimmersion fluid and photoresist interfaces, for example, an improvedwater receding contact angle at the immersion fluid interface and gooddeveloper solubility at the photoresist interface.

Topcoats exhibiting a low receding contact angle for a given scan speedcan result in water mark defects. These defects are generated when waterdroplets are left behind as the exposure head moves across the wafer. Asa result, resist sensitivity becomes altered due to leaching of resistcomponents into the water droplets, and water can permeate into theunderlying resist. Topcoats having high receding contact angles wouldtherefore be desired to allow for operation of immersion scanners atgreater scan speeds, thereby allowing for increased process throughput.U.S. Patent App. Pub. Nos. 2007/0212646A1 to Gallagher et al. and2010/0183976A1 to Wang et al. describe immersion topcoat compositionsthat include a self-segregating surface active polymer which allow forimproved water receding contact angles. With the desire for increasinglyfaster scan speeds on the exposure tool to allow for increasedthroughput, topcoat compositions having further improved recedingcontact angles are desired.

There is a continuing need in the art for topcoat compositionsexhibiting high receding contact angles for use in immersionlithography, and for photolithographic methods making use of suchmaterials.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, provided arephotoresist topcoat compositions. The compositions comprise: a firstpolymer comprising a first repeat unit of general formula (I) and asecond repeat unit of general formula (II):

wherein: R₁ independently represents H, F or optionally fluorinated C1to C4 alkyl; R₂ represents optionally fluorinated linear, branched orcyclic C1 to C20 alkyl; L₁ represents a single bond or a multivalentlinking group; and n is an integer of from 1 to 5; a second polymercomprising a first repeat unit of general formula (III) and a secondrepeat unit of general formula (IV):

wherein: R₃ independently represents H, F or optionally fluorinated C1to C4 alkyl; R₄ represents linear, branched or cyclic C1 to C20 alkyl;R₅ represents linear, branched or cyclic C1 to C20 fluoroalkyl; L₂represents a single bond or a multivalent linking group; and n is aninteger of from 1 to 5; and a solvent.

In accordance with a further aspect of the invention, provided arecoated substrates. The coated substrates comprise: a photoresist layeron a substrate; and a topcoat layer formed from a photoresist topcoatcomposition as described herein on the photoresist layer.

In accordance with a further aspect of the invention, provided aremethods of processing a photoresist composition. The methods comprise:(a) applying a photoresist composition over a substrate to form aphotoresist layer; (b) applying over the photoresist layer a photoresisttopcoat composition as described herein to form a topcoat layer; (c)exposing the topcoat layer and the photoresist layer to activatingradiation; and (d) contacting the exposed topcoat layer and photoresistlayer with a developer to form a resist pattern.

DETAILED DESCRIPTION

The topcoat compositions of the invention comprise a matrix polymer, asurface active polymer, a solvent, and can include one or moreadditional, optional components. The surface active polymer has a lowersurface energy than that of the matrix polymer and other polymers in thecomposition.

Topcoat compositions of the invention that are applied above aphotoresist layer are self-segregating, and can minimize or preventmigration of components of the photoresist layer into an immersion fluidemployed in an immersion lithography process. As used herein, the term“immersion fluid” means a fluid, typically water, interposed between alens of an exposure tool and a photoresist coated substrate to conductimmersion lithography.

Also as used herein, a topcoat layer will be considered as inhibitingthe migration of photoresist material into an immersion fluid if adecreased amount of acid or organic material is detected in theimmersion fluid upon use of the topcoat composition relative to the samephotoresist system that is processed in the same manner, but in theabsence of the topcoat composition layer. Detection of photoresistmaterial in the immersion fluid can be conducted through massspectroscopy analysis of the immersion fluid before exposure to thephotoresist (with and without the overcoated topcoat composition layer)and then after lithographic processing of the photoresist layer (withand without the overcoated topcoat composition layer) with exposurethrough the immersion fluid. Preferably, the topcoat compositionprovides at least a 10 percent reduction in photoresist material (e.g.,acid or organics as detected by mass spectroscopy) residing in theimmersion fluid relative to the same photoresist that does not employany topcoat layer (i.e., the immersion fluid directly contacts thephotoresist layer), more preferably the topcoat composition provides atleast a 20, 50, or 100 percent reduction in photoresist materialresiding in the immersion fluid relative to the same photoresist thatdoes not employ a topcoat layer.

Topcoat compositions of the invention can allow for improvement in oneor more of various water contact angle characteristics that areimportant in an immersion lithography process, for example, staticcontact angle, receding contact angle, advancing contact angle andsliding angle at the immersion fluid interface. The topcoat compositionsprovide topcoat layers having excellent developer solubility for bothexposed and unexposed regions of the layer, for example, in an aqueousbase developer.

The compositions can be used in dry lithography or more typically inimmersion lithography processes. The exposure wavelength is notparticularly limited except by the photoresist compositions, with 248 nmor sub 200 nm such as 193 nm or an EUV wavelength (e.g., 13.4 nm) beingtypical.

Polymers useful in the invention are preferably aqueous alkali solublesuch that a topcoat layer formed from the composition can be removed inthe resist development step using an aqueous alkaline developer, forexample, a quaternary ammonium hydroxide solution, for example,tetramethylammonium hydroxide (TMAH). The different polymers suitablymay be present in varying relative amounts.

The polymers of the topcoat compositions of the invention may contain avariety of repeat units, including, for example, one or more:hydrophobic groups; weak acid groups; strong acid groups; branchedoptionally substituted alkyl or cycloalkyl groups; fluoroalkyl groups;or polar groups, such as ester, ether, carboxy, or sulfonyl groups. Thepresence of particular functional groups on the repeat units of thepolymers will depend, for example, on the intended functionality of thepolymer.

One or more polymers of the topcoat composition can comprise one or moregroups that are reactive during lithographic processing, for example,one or more photoacid-labile groups that can undergo cleavage reactionsin the presence of acid and heat, such as acid-labile ester groups(e.g., t-butyl ester groups such as provided by polymerization oft-butyl acrylate or t-butylmethacrylate, adamantylacrylate) and/oracetal groups such as provided by polymerization of a vinyl ethercompound. The presence of such groups can render the associatedpolymer(s) more soluble in a developer solution, thereby aiding indevelopability and removal of the topcoat layer during a developmentprocess.

The polymers can advantageously be selected to tailor characteristics ofthe topcoat layer, with each generally serving one or more purpose orfunction. Such functions include, for example, one or more ofphotoresist profile adjusting, topcoat surface adjusting, reducingdefects and reducing interfacial mixing between the topcoat andphotoresist layers.

The matrix polymer comprises a repeat unit of general formula (I) and arepeat unit of general formula (II):

wherein: R₁ independently represents H, F or optionally fluorinated C1to C4 alkyl, typically H or methyl; R₂ represents optionally fluorinatedlinear, branched or cyclic C1 to C20 alkyl, typically C1 to C12 alkyl;L₁ represents a single bond or a multivalent linking group chosen, forexample, from optionally substituted aliphatic, such as C1 to C6alkylene, and aromatic hydrocarbons, and combinations thereof,optionally with one or more linking moieties chosen from —O—, —S—, —COO—and —CONR— wherein R is chosen from hydrogen and optionally substitutedC1 to C10 alkyl; and n is an integer of from 1 to 5, typically 1.

It is believed that units of general formula (I) allow for goodsolubility of the matrix polymer in the solvent used in the topcoatcomposition. Due to their highly polar nature, units of general formula(II) can impart desirable solubility characteristics to the matrixpolymer in an aqueous base developer. This allows for effective removalduring photoresist development.

Units of general formula (I) are typically present in the matrix polymerin an amount of from 1 to 90 mol %, typically from 50 to 80 mol %, basedon the matrix polymer. Units of general formula (II) are typicallypresent in the matrix polymer in an amount of from 1 to 90 mol %,typically, from 10 to 50 mol %, based on the matrix polymer.

Exemplary suitable monomers for forming units of general formula (I)include the following:

Exemplary suitable monomers for forming units of general formula (II)including the following:

The matrix polymer may include one or more additional units of generalformula (I), general formula (II) and/or an additional type of unit. Thematrix polymer may, for example, include a unit containing a sulfonamidegroup (e.g., —NHSO₂CF₃), a fluoroalkyl group and/or a fluoroalcoholgroup (e.g., —C(CF₃)₂OH) for enhancing developer dissolution rate of thepolymer. Additional types of units, if used, are typically present inthe matrix polymer in an amount of from 1 to 40 mol % based on thematrix polymer.

The matrix polymer should provide a sufficiently high developerdissolution rate for reducing overall defectivity due, for example, tomicro-bridging. A typical developer dissolution rate for the matrixpolymer is greater than 300 nm/second, preferably greater than 1000nm/second and more preferably greater than 3000 nm/second.

The matrix polymer preferably has a higher surface energy than that of,and is preferably substantially immiscible with, the surface activepolymer, to allow the surface active polymer to phase separate from thematrix polymer and migrate to the upper surface of the topcoat layeraway from the topcoat layer/photoresist layer interface. The surfaceenergy of the matrix polymer is typically from 30 to 60 mN/m.

Exemplary matrix polymers in accordance with the invention include thefollowing:

The matrix polymer is typically present in the compositions in an amountof from 70 to 99 wt %, more typically from 85 to 95 wt %, based on totalsolids of the topcoat composition. The weight average molecular weightof the matrix polymer is typically less than 400,000, for example, from5000 to 50,000 or from 5000 to 25,000.

The surface active polymer is provided in the topcoat compositions toimprove surface properties at the topcoat/immersion fluid interface inthe case of an immersion lithography process. In particular, the surfaceactive polymer beneficially can provide desirable surface propertieswith respect to water, for example, one or more of improved staticcontact angle (SCA), receding contact angle (RCA), advancing contactangle (ACA) and sliding angle (SA) at the topcoat layer/immersion fluidinterface. In particular, the surface active polymers can allow forhigher RCAs, which can allow for faster scanning speeds and increasedprocess throughput. A layer of the topcoat composition in a dried statetypically has a water receding contact angle of from 75 to 900, andpreferably from 80 to 900 and more preferably from 83 to 900, forexample, from 83 to 880. The phrase “in a dried state” means containing8 wt % or less of solvent, based on the entire topcoat composition.

The surface active polymer is preferably aqueous alkali soluble to allowfor complete removal during development with an aqueous base developer.The surface active polymer is preferably free of carboxylic acid groupsas such groups can reduce the receding contact angle properties of thepolymer.

The surface active polymer has a lower surface energy than the matrixpolymer. Preferably, the surface active polymer has a significantlylower surface energy than and is substantially immiscible with thematrix polymer, as well as other polymers present in the overcoatcomposition. In this way, the topcoat composition can beself-segregating, wherein the surface active polymer migrates to theupper surface of the topcoat layer apart from other polymer(s) duringcoating, typically spin-coating. The resulting topcoat layer is therebyrich in the surface active polymer at the topcoat layer upper surface atthe topcoat/immersion fluid interface in the case of an immersionlithography process. The surface active polymer-rich surface region istypically from one to two or from one to three monolayers in thickness,or about 10 to 20 Å in thickness. While the desired surface energy ofthe surface active polymer will depend on the particular matrix polymerand its surface energy, the surface active polymer surface energy istypically from 15 to 35 mN/m, preferably from 18 to 30 mN/m. The surfaceactive polymer is typically from 5 to 25 mN/m less than that of thematrix polymer, preferably from 5 to 15 mN/m less than that of thematrix polymer.

The surface active polymer comprises a repeat unit of general formula(III) and a repeat unit of general formula (IV):

wherein: R₃ independently represents H, F or optionally fluorinated C1to C4 alkyl, typically H or methyl; R₄ represents linear, branched orcyclic C1 to C20 alkyl, typically C1 to C12 alkyl; R₅ represents linear,branched or cyclic C1 to C20 fluoroalkyl, typically C1 to C12fluoroalkyl; L₂ represents a single bond or a multivalent linking groupchosen, for example, from optionally substituted aliphatic, such as C1to C6 alkylene, and aromatic hydrocarbons, and combinations thereof,optionally with one or more linking moieties chosen from —O—, —S—, —COO—and —CONR— wherein R is chosen from hydrogen and optionally substitutedC1 to C10 alkyl, L₁ preferably being —C(O)OCH₂—; and n is an integer offrom 1 to 5, typically 1.

Units formed from monomers of general formula (III) containing an alkylgroup are believed to impart beneficial hysteresis characteristics tothe surface active polymer, for example, providing desirable wateraffinity and developer wetting properties. It is believed that monomersof general formula (IV) allow for effective phase separation of thesurface active polymer from other polymers in the composition, enhanceddynamic contact angles, for example, increased receding angle anddecreased sliding angle, as well as improving developer affinity andsolubility.

Units of general formula (III) are typically present in the surfaceactive polymer in an amount of from 1 to 90 mol %, for example, from 50to 80 mol %, based on the surface active polymer. Units of generalformula (IV) are typically present in the surface active polymer in anamount of from 1 to 90 mol %, for example, from 10 to 40 mol %, based onthe surface active polymer.

Exemplary suitable monomers for the units of general formula (III)include the following:

Exemplary suitable monomers for the units of general formula (IV)include the following:

The surface active polymer may include one or more additional units ofgeneral formula (III), general formula (IV) and/or an additional type ofunit. The surface active polymer can, for example, include one or moreadditional units comprising a fluorine-containing group, such as afluorinated sulfonamide group, a fluorinated alcohol group, afluorinated ester group, or a combination thereof, or an acid-labileleaving group, or a combination thereof. Fluoroalcohol group-containingunits can be present in the surface active polymer for purposes ofenhancing developer solubility, or to allow for enhanced dynamic contactangles, for example, increased receding angle and decreased slidingangle, and for improving developer affinity and solubility. Additionaltypes of units, if used, are typically present in the surface activepolymer in an amount of from 1 to 70 mol % based on the surface activepolymer.

Exemplary polymers useful as the surface active polymer include, forexample, the following:

The lower content limit for the surface active polymer for immersionlithography is generally dictated by the need to prevent leaching of thephotoresist components. The surface active polymer is typically presentin the compositions in an amount of from 1 to 30 wt %, more typicallyfrom 3 to 20 wt % or 5 to 15 wt %, based on total solids of the topcoatcomposition. The weight average molecular weight of the surface activepolymer is typically less than 400,000, preferably from 5000 to 50,000,more preferably from 5000 to 25,000.

Optional additional polymers can be present in the topcoat compositions.An additive polymer can, for example, be provided in addition to thematrix polymer and the surface active polymer for purposes of tuning theresist feature profile and/or for controlling resist top loss. Theadditive polymer should be miscible with the matrix polymer, andsubstantially immiscible with the surface active polymer such that thesurface active polymer can self-segregate from the additive polymer tothe topcoat surface away from the topcoat/photoresist interface.

Preferred additive polymers comprises a repeat unit of general formula(V) and a repeat unit of general formula (VI):

wherein: R₆ independently represents H, F, and optionally fluorinated C1to C4 alkyl, typically H or methyl; R₇ represents linear, branched orcyclic C1 to C20 alkyl, typically C1 to C12 alkyl; and R₈ represents alinear, branched or cyclic C1 to C20 fluoroalkyl, typically C1 to C12fluoroalkyl.

Units of general formula (V) are typically present in the additivepolymer in an amount of from 1 to 90 mol %, for example, from 50 to 80mol %, based on the additive polymer, and units of general formula (VI)are typically present in the additive polymer in an amount of from 1 to90 mol %, for example, from 50 to 80 mol %, based on the additivepolymer.

Exemplary suitable monomers for the units of general formula (V) includethe following:

Exemplary suitable monomers for the units of general formula (VI)include the following:

The additive polymer, if used, is typically present in the compositionsin an amount of from 1 to 40 wt %, more typically from 3 to 20 wt % or 5to 15 wt %, based on total solids of the topcoat composition. The weightaverage molecular weight of the additive polymer is typically less than400,000, preferably from 5000 to 50,000, more preferably from 5000 to25,000.

Exemplary polymers useful as the additive polymer include, for example,the following:

Typical solvent materials to formulate and cast a topcoat compositionare any which dissolve or disperse the components of the topcoatcomposition but do not appreciably dissolve an underlying photoresistlayer. Preferably, a mixture of different solvents, for example, two,three or more solvents, can be used to achieve effective phaseseparation of the segregating, surface active polymer from otherpolymer(s) in the composition. A solvent mixture can also be effectiveto reduce the viscosity of the formulation which allows for reduction inthe dispense volume.

In an exemplary aspect, a two-solvent system or a three-solvent systemcan be used in the topcoat compositions of the invention. A preferredsolvent system includes a primary solvent and an additive solvent, andmay include a thinner solvent. The primary solvent typically exhibitsexcellent solubility characteristics with respect to the non-solventcomponents of the topcoat composition. While the desired boiling pointof the primary solvent will depend on the other components of thesolvent system, the boiling point is typically less than that of theadditive solvent, with a boiling point of from 120 to 140° C. such asabout 130° C. being typical. Suitable primary solvents include, forexample, C4 to C10 monovalent alcohols, such as n-butanol, isobutanol,2-methyl-1-butanol, isopentanol, 2,3-dimethyl-1-butanol,4-methyl-2-pentanol, isohexanol, isoheptanol, 1-octanol, 1-nonanol and1-decanol, and mixtures thereof. The primary solvent is typicallypresent in an amount of from 30 to 80 wt % based on the solvent system.

The additive solvent can facilitate phase separation between the surfaceactive polymer and other polymer(s) in the topcoat composition tofacilitate a self-segregating topcoat structure. In addition, the higherboiling point additive solvent can reduce the tip drying effect duringcoating. It is typical for the additive solvent to have a higher boilingpoint than the other components of the solvent system. While the desiredboiling point of the additive solvent will depend on the othercomponents of the solvent system, a boiling point of from 170 to 200° C.such as about 190° C. is typical. Suitable additive solvents include,for example, hydroxy alkyl ethers such as those of the formula:

R₁₁—O—R₁₂—O—R₁₃—OH

wherein R₁₁ is an optionally substituted C1 to C2 alkyl group and R₁₂and R₁₃ are independently chosen from optionally substituted C2 to C4alkyl groups, and mixtures of such hydroxy alkyl ethers includingisomeric mixtures. Exemplary hydroxy alkyl ethers include dialkyl glycolmono-alkyl ethers and isomers thereof, for example, diethylene glycolmonomethyl ether, dipropylene glycol monomethyl ether, isomers thereofand mixtures thereof. The additive solvent is typically present in anamount of from 3 to 15 wt % based on the solvent system.

A thinner solvent can be used to lower the viscosity and improve coatingcoverage at a lower dispensing volume. The thinner solvent is typicallya poorer solvent for the non-solvent components of the compositionrelative to the primary solvent. While the desired boiling point of thethinner solvent will depend on the other components of the solventsystem, a boiling point of from 140 to 180° C. such as about 170° C. istypical. Suitable thinner solvents include, for example, alkanes such asC8 to C12 n-alkanes, for example, n-octane, n-decane and dodecane,isomers thereof and mixtures of isomers thereof; and/or alkyl etherssuch as those of the formula R₁₄—O—R₁₅, wherein R₁₄ and R₁₅ areindependently chosen from C2 to C8 alkyl, C2 to C6 alkyl and C2 to C4alkyl. The alkyl ether groups can be linear or branched, and symmetricor asymmetric. Particularly suitable alkyl ethers include, for example,isobutyl ether, isopentyl ether, isobutyl isohexyl ether, and mixturesthereof. Other suitable thinner solvents include ester solvents, forexample, those represented by general formula (VII):

wherein: R₁₆ and R₁₇ are independently chosen from C3 to C8 alkyl; andthe total number of carbon atoms in R₁₆ and R₁₇ taken together isgreater than 6. Suitable such ester solvents include, for example,propyl pentanoate, isopropyl pentanoate, isopropyl 3-methylbutanoate,isopropyl 2-methylbutanoate, isopropyl pivalate, isobutyl isobutyrate,2-methylbutyl isobutyrate, 2-methylbutyl 2-methylbutanoate,2-methylbutyl 2-methylhexanoate, 2-methylbutyl heptanoate, hexylheptanoate, n-butyl n-butyrate, isoamyl n-butyrate and isoamylisovalerate. The thinner solvent if used is typically present in anamount of from 10 to 70 wt % based on the solvent system.

A particularly preferred solvent system includes 4-methyl-2-pentanol,dipropylene glycol methyl ether and isobutyl isobutyrate. While theexemplary solvent system has been described with respect to two- andthree-component systems, it should be clear that additional solvents maybe used. For example, one or more additional primary solvents, thinnersolvents, additive solvents and/or other solvents may be employed.

The topcoat compositions may comprise one or more other optionalcomponents. For example, the compositions can include one or more ofactinic and contrast dyes for enhancing antireflective properties,anti-striation agents, and the like. Such optional additives if used aretypically present in the composition in minor amounts such as from 0.1to 10 wt % based on total solids of the overcoat composition.

It may be beneficial to include an acid generator compound such as aphotoacid generator (PAG) compound in the topcoat compositions. Suitablephotoacid generators are known in the art of chemically amplifiedphotoresists and include, for example: onium salts, for example,triphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate; nitrobenzyl derivatives, forexample, 2-nitrobenzyl-p-toluenesulfonate,2,6-dinitrobenzyl-p-toluenesulfonate, and2,4-dinitrobenzyl-p-toluenesulfonate; sulfonic acid esters, for example,1,2,3-tris(methanesulfonyloxy)benzene,1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and1,2,3-tris(p-toluenesulfonyloxy)benzene; diazomethane derivatives, forexample, bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane; glyoxime derivatives, for example,bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime, andbis-O-(n-butanesulfonyl)-α-dimethylglyoxime; sulfonic acid esterderivatives of an N-hydroxyimide compound, for example,N-hydroxysuccinimide methanesulfonic acid ester, N-hydroxysuccinimidetrifluoromethanesulfonic acid ester; and halogen-containing triazinecompounds, for example,2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, and2-(4-methoxynaphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine. One ormore of such PAGs can be used. If employed, the one or more acidgenerators may be utilized in relatively small amounts in a topcoatcomposition, for example, from 0.1 to 8 wt %, based on total solids ofthe composition. Such use of one or more acid generator compounds mayfavorably impact lithographic performance, particularly resolution, ofthe developed image patterned in an underlying resist layer.

Topcoat layers formed from the compositions typically have an index ofrefraction of 1.4 or greater at 193 nm, preferably 1.47 or greater at193 nm. The index of refraction can be tuned by changing the compositionof the matrix polymer, the surface active polymer, the additive polymeror other components of the overcoat composition. For example, increasingthe relative amount of organic content in the overcoat composition mayprovide increased refractive index of the layer. Preferred overcoatcomposition layers will have a refractive index between that of theimmersion fluid and the photoresist at the target exposure wavelength.

The photoresist topcoat compositions can be prepared following knownprocedures. For example, the compositions can be prepared by dissolvingsolid components of the composition in the solvent components. Thedesired total solids content of the compositions will depend on factorssuch as the particular polymers in the composition and desired finallayer thickness. Preferably, the solids content of the overcoatcompositions is from 1 to 10 wt %, more preferably from 1 to 5 wt %,based on the total weight of the composition. The viscosity of theentire composition is typically from 1.5 to 2 centipoise (cp).

Photoresists

Photoresist compositions useful in the invention includechemically-amplified photoresist compositions comprising a matrixpolymer that is acid-sensitive, meaning that as part of a layer of thephotoresist composition, the polymer and composition layer undergo achange in solubility in a developer as a result of reaction with acidgenerated by a photoacid generator following softbake, exposure toactivating radiation and post exposure bake. The resist formulation canbe positive-acting or negative-acting, but is typically positive-acting.In positive-type photoresists, the change in solubility is typicallybrought about when acid-labile groups such as photoacid-labile ester oracetal groups in the matrix polymer undergo a photoacid-promoteddeprotection reaction on exposure to activating radiation and heattreatment. Suitable photoresist compositions useful for the inventionare commercially available

For imaging at wavelengths such as 193 nm, the matrix polymer istypically substantially free (e.g., less than 15 mole %) or completelyfree of phenyl, benzyl or other aromatic groups where such groups arehighly absorbing of the radiation. Suitable polymers that aresubstantially or completely free of aromatic groups are disclosed inEuropean application EP930542A1 and U.S. Pat. Nos. 6,692,888 and6,680,159, all of the Shipley Company. Preferable acid-labile groupsinclude, for example, acetal groups or ester groups that contain atertiary non-cyclic alkyl carbon (e.g., t-butyl) or a tertiary alicycliccarbon (e.g., methyladamantyl) covalently linked to a carboxyl oxygen ofan ester of the matrix polymer.

Suitable matrix polymers further include polymers that contain(alkyl)acrylate units, preferably including acid-labile (alkyl)acrylateunits, such as t-butyl acrylate, t-butyl methacrylate, methyladamantylacrylate, methyladamantyl methacrylate, ethylfenchyl acrylate,ethylfenchyl methacrylate, and the like, and other non-cyclic alkyl andalicyclic (alkyl)acrylates. Such polymers have been described, forexample, in U.S. Pat. No. 6,057,083, European Published ApplicationsEP01008913A1 and EP00930542A1, and U.S. Pat. No. 6,136,501. Othersuitable matrix polymers include, for example, those which containpolymerized units of a non-aromatic cyclic olefin (endocyclic doublebond) such as an optionally substituted norbornene, for example,polymers described in U.S. Pat. Nos. 5,843,624 and 6,048,664. Stillother suitable matrix polymers include polymers that contain polymerizedanhydride units, particularly polymerized maleic anhydride and/oritaconic anhydride units, such as disclosed in European PublishedApplication EP01008913A1 and U.S. Pat. No. 6,048,662.

Also suitable as the matrix polymer is a resin that contains repeatunits that contain a heteroatom, particularly oxygen and/or sulfur (butother than an anhydride, i.e., the unit does not contain a keto ringatom). The heteroalicyclic unit can be fused to the polymer backbone,and can comprise a fused carbon alicyclic unit such as provided bypolymerization of a norbornene group and/or an anhydride unit such asprovided by polymerization of a maleic anhydride or itaconic anhydride.Such polymers are disclosed in PCT/US01/14914 and U.S. Pat. No.6,306,554. Other suitable heteroatom group-containing matrix polymersinclude polymers that contain polymerized carbocyclic aryl unitssubstituted with one or more heteroatom (e.g., oxygen or sulfur)containing groups, for example, hydroxy naphthyl groups, such asdisclosed in U.S. Pat. No. 7,244,542.

Blends of two or more of the above-described matrix polymers cansuitably be used in the photoresist compositions.

Suitable matrix polymers for use in the photoresist compositions arecommercially available and can be readily made by persons skilled in theart. The matrix polymer is present in the resist composition in anamount sufficient to render an exposed coating layer of the resistdevelopable in a suitable developer solution. Typically, the matrixpolymer is present in the composition in an amount of from 50 to 95 wt %based on total solids of the resist composition. The weight averagemolecular weight M_(w) of the matrix polymer is typically less than100,000, for example, from 5000 to 100,000, more typically from 5000 to15,000.

The photoresist composition further comprises a photoactive componentsuch as a photoacid generator (PAG) employed in an amount sufficient togenerate a latent image in a coating layer of the composition uponexposure to activating radiation. For example, the photoacid generatorwill suitably be present in an amount of from about 1 to 20 wt % basedon total solids of the photoresist composition. Typically, lesseramounts of the PAG will be suitable for chemically amplified resists ascompared with non-chemically amplified materials. Suitable PAGs areknown in the art of chemically amplified photoresists and include, forexample, those described above with respect to the topcoat composition.

Suitable solvents for the photoresist compositions include, for example:glycol ethers such as 2-methoxyethyl ether (diglyme), ethylene glycolmonomethyl ether, and propylene glycol monomethyl ether; propyleneglycol monomethyl ether acetate; lactates such as methyl lactate andethyl lactate; propionates such as methyl propionate, ethyl propionate,ethyl ethoxy propionate and methyl-2-hydroxy isobutyrate; Cellosolveesters such as methyl Cellosolve acetate; aromatic hydrocarbons such astoluene and xylene; and ketones such as acetone, methylethyl ketone,cyclohexanone and 2-heptanone. A blend of solvents such as a blend oftwo, three or more of the solvents described above also are suitable.The solvent is typically present in the composition in an amount of from90 to 99 wt %, more typically from 95 to 98 wt %, based on the totalweight of the photoresist composition.

The photoresist compositions can also include other optional materials.For example, the compositions can include one or more of actinic andcontrast dyes, anti-striation agents, plasticizers, speed enhancers,sensitizers, and the like. Such optional additives if used are typicallypresent in the composition in minor amounts such as from 0.1 to 10 wt %based on total solids of the photoresist composition.

A preferred optional additive of the resist compositions is an addedbase. Suitable bases are known in the art and include, for example,linear and cyclic amides and derivatives thereof such asN,N-bis(2-hydroxyethyl)pivalamide, N,N-Diethylacetamide,N1,N1,N3,N3-tetrabutylmalonamide, 1-methylazepan-2-one,1-allylazepan-2-one and tert-butyl1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylcarbamate; aromatic aminessuch as pyridine, and di-tert-butyl pyridine; aliphatic amines such astriisopropanolamine, n-tert-butyldiethanolamine, tris(2-acetoxy-ethyl)amine, 2,2′,2″,2′″-(ethane-1,2-diylbis(azanetriyl))tetraethanol, and2-(dibutylamino)ethanol, 2,2′,2″-nitrilotriethanol; cyclic aliphaticamines such as 1-(tert-butoxycarbonyl)-4-hydroxypiperidine, tert-butyl1-pyrrolidinecarboxylate, tert-butyl 2-ethyl-1H-imidazole-1-carboxylate,di-tert-butyl piperazine-1,4-dicarboxylate and N (2-acetoxy-ethyl)morpholine. The added base is suitably used in relatively small amounts,for example, from 0.01 to 5 wt %, preferably from 0.1 to 2 wt %, basedon total solids of the photoresist composition.

The photoresists can be prepared following known procedures. Forexample, the resists can be prepared as coating compositions bydissolving the solid components of the photoresist in the solventcomponent. The desired total solids content of the photoresist willdepend on factors such as the particular polymers in the composition,final layer thickness and exposure wavelength. Typically the solidscontent of the photoresist varies from 1 to 10 wt %, more typically from2 to 5 wt %, based on the total weight of the photoresist composition.

Lithographic Processing

Liquid photoresist compositions can be applied to a substrate such as byspin-coating, dipping, roller-coating or other conventional coatingtechnique, with spin-coating being typical. When spin coating, thesolids content of the coating solution can be adjusted to provide adesired film thickness based upon the specific spinning equipmentutilized, the viscosity of the solution, the speed of the spinner andthe amount of time allowed for spinning.

Photoresist compositions used in the methods of the invention aresuitably applied to a substrate in a conventional manner for applyingphotoresists. For example, the compositions may be applied over siliconwafers or silicon wafers coated with one or more layers and havingfeatures on a surface for the production of microprocessors or otherintegrated circuit components. Aluminum-aluminum oxide, galliumarsenide, ceramic, quartz, copper, glass substrates and the like mayalso be suitably employed. The photoresist compositions are typicallyapplied over an antireflective layer, for example, an organicantireflective layer.

A topcoat composition of the invention can be applied over thephotoresist composition by any suitable method such as described abovewith reference to the photoresist compositions, with spin-coating beingtypical.

Following coating of the photoresist onto a surface, it may be heated(softbaked) to remove the solvent until typically the photoresistcoating is tack free, or the photoresist layer may be dried after thetopcoat composition has been applied and the solvent from both thephotoresist composition and topcoat composition layers substantiallyremoved in a single thermal treatment step.

The photoresist layer with overcoated topcoat layer is then exposedthrough a patterned photomask to radiation activating for thephotoactive component of the photoresist. The exposure is typicallyconducted with an immersion scanner but can alternatively be conductedwith a dry (non-immersion) exposure tool.

During the exposure step, the photoresist composition layer is exposedto patterned activating radiation with the exposure energy typicallyranging from about 1 to 100 mJ/cm², dependent upon the exposure tool andthe components of the photoresist composition. References herein toexposing a photoresist composition to radiation that is activating forthe photoresist indicates that the radiation is capable of forming alatent image in the photoresist such as by causing a reaction of thephotoactive component, for example, producing photoacid from a photoacidgenerator compound.

The photoresist composition (and topcoat composition if photosensitive)is typically photoactivated by a short exposure wavelength, for example,radiation having a wavelength of less than 300 nm such as 248 nm, 193 nmand EUV wavelengths such as 13.5 nm. Following exposure, the layer ofthe composition is typically baked at a temperature ranging from about70° C. to about 160° C.

Thereafter, the film is developed, typically by treatment with anaqueous base developer chosen, for example, from: quaternary ammoniumhydroxide solutions such as a tetra-alkyl ammonium hydroxide solutions,typically a 0.26 N tetramethylammonium hydroxide; amine solutions suchas ethyl amine, n-propyl amine, diethyl amine, di-n-propyl amine,triethyl amine, or methyldiethyl amine; alcohol amines such as diethanolamine or triethanol amine; and cyclic amines such as pyrrole orpyridine. In general, development is in accordance with proceduresrecognized in the art.

Following development of the photoresist layer, the developed substratemay be selectively processed on those areas bared of resist, for exampleby chemically etching or plating substrate areas bared of resist inaccordance with procedures known in the art. After such processing, theresist remaining on the substrate can be removed from the using knownstripping procedures.

The following non-limiting examples are illustrative of the invention.

Examples

Number and weight-average molecular weights, Mn and Mw, andpolydispersity values, Mw/Mn or PDI, were measured by gel permeationchromatography (GPC) on an Agilent 1100 series LC system equipped withan Agilent 1100 series refractive index and MiniDAWN light scatteringdetector (Wyatt Technology Co.). Samples were dissolved in HPCL gradeTHF at a concentration of approximately 1 mg/mL and filtered through at0.20 m syringe filter before injection through the GPC column. A flowrate of 1 mL/min and temperature of 35° C. were maintained. The columnswere calibrated with narrow molecular weight PS standards (EasiCal PS-2,Polymer Laboratories, Inc.).

Polymer Synthesis and Characterization

The following monomers were used to prepare matrix polymers, surfaceactive polymers and additive polymers for topcoat compositions asdescribed below:

Matrix Polymer (MP) Synthesis

A monomer feed solution was prepared by combining 10 g4-methyl-2-pentanol (4M2P), 6 g monomer M1 and 4 g monomer M4 in acontainer, and agitating the mixture to dissolve the two monomers. Aninitiator feed solution was prepared by combining 0.61 g Wako V-601initiator and 6.2 g 4M2P in a suitable container and agitating themixture to dissolve the initiator. 13.3 g 4M2P was introduced into areaction vessel and the vessel was purged with nitrogen for 30 minutes.The reaction vessel was next heated to 88° C. with agitation.Introduction of the monomer feed solution and initiator feed solutioninto the reaction vessel was simultaneously started. The monomer feedsolution was fed over a period of 1.5 hours and the initiator feedsolution over a period of two hours. The reaction vessel was maintainedat 88° C. for an additional three hours with agitation, and then allowedto cool to room temperature. Polymer MP4 [Mw=13.6 kDa and PID=2.4] wasthereby formed.

Polymers MP1 to MP3 were synthesized employing a procedure similar tothat used for MP4, using the monomers and amounts (as mole fractions)set forth in Table 1.

TABLE 1 Matrix DR Polymer M1 M2 M3 M4 Mw PDI Å/s MP1 25 21 54   13K 2.836,620 MP2 43 57 17.6K 3.0 43,180 MP3 25 21 54 19.6K 2.5 36,720 MP4 4852 13.6K 2.4 36,660

Surface Active Polymer (SAP) and Additive Polymer (AP) Synthesis

A monomer feed solution was prepared by combining 57.1 g monomer M5,50.7 g monomer M7 and 15.1 g propylene glycol monomethyl ether acetate(PGMEA) in a container. The mixture was agitated to dissolve themonomers. An initiator feed solution was prepared by combining 3.9 gWako V-601 initiator (E. I. du Pont de Nemours and Company) and 34.9 gPGMEA in a container. The mixture was agitated to dissolve theinitiator. 54.0 g PGMEA was introduced into a reaction vessel and thevessel was purged with nitrogen for 30 minutes. The reaction vessel wasnext heated to 99° C. with agitation. The monomer feed solution andinitiator feed solution were simultaneously introduced into the reactionvessel for a period of two hours. The reaction vessel was maintained at99° C. for an additional two hours. The reaction mixture was thenallowed to cool to room temperature. Polymer SAP1 [Mn=11.7 kDa andPDI=2.0] was thereby formed.

Polymers SAP2 to SAP-3 and API to AP7 were synthesized employing aprocedure similar to that used for Polymer SAP1, using the monomers andamounts (as mole fractions) set forth in Table 2 for the Surface ActivePolymers and in Table 3 for the Additive Polymers.

TABLE 2 Surface Active DR Polymer M2 M4 M5 M6 M7 Mw PDI Å/s SAP1 70 3011.7K 2.0 0 SAP2 30 70   9K 1.7 0 SAP3 30 70 13.5K 1.7 0

TABLE 3 Additive DR Polymer M2 M4 M5 M6 M8 Mw PDI Å/s AP1 24 18 58 10.4K1.8 0.05 AP2 26 22 52 11.2K 1.9 35 AP3 25 57 18 10.8K 2.0 43 AP4 18 5725 12.1K 2.1 360

Dissolution Rate Measurements

On a TEL ACT-8 wafer track, 8-inch silicon wafers were primed with HMDSat 120° C. for 30 seconds, coated with a 14 wt % solution of arespective matrix, surface active or additive polymer in PGMEA andsoftbaked at 90° C. for 60 seconds. Dissolution rate (DR) was measuredin MF™-312 TMAH developer (Rohm and Haas Electronic Materials) at 22° C.on an LTJ ARM-808EUV dissolution rate monitor at 470 nm wavelength. Theresults are shown in Tables 1-3.

Topcoat Composition Preparation and Characterization

Topcoat compositions were prepared by admixing the components in theamounts set forth in Table 4. The compositions were filtered through 0.2m PTFE disk filters prior to use.

TABLE 4 Ex. MP SAP AP Acid PAG 4M2P IBIB DPM RCA  1 MP1 SAP1 A1 0.00855.8 40.1 2.0 85.4   1.334 0.185 0.023  2 MP2 SAP1 A1 0.008 55.8 40.12.0 84.4   1.334 0.185 0.023  3 MP3 SAP1 0.008 55.8 40.1 2.0 85.3  1.334 0.185  4 MP4 SAP1 A1 0.007 55.9 40.2 2.0 85.9   1.248 0.173 0.022 5 MP4 SAP1 A1 0.014 56.1 40.3 2.0 84.7   1.219 0.173 0.044  6 MP4 SAP20.014 56.1 40.3 2.0 87.2   1.219 0.173  7 MP4 SAP2 AP1 A1 0.014 56.140.3 2.0 83.5   1.219 0.052 0.121 0.044  8 MP4 SAP2 AP2 A1 0.014 56.140.3 2.0 81.1   1.219 0.052 0.121 0.044  9 MP4 SAP3 A1 0.014 56.1 40.32.0 83.1 1.340 0.052 0.044 10 

MP4 SAP3 AP3 A1 0.014 56.1 40.3 2.0 85.4 1.219 0.052 0.121 0.044 11 

MP4 SAP3 AP4 0.014 56.1 40.3 2.0 85.4 1.219 0.052 0.121 Comp. MP4 0.01456.1 40.3 2.0 33.0 Ex. 1 1.392 Comp. MP4 AP2 0.014 56.1 40.3 2.0 66.1Ex. 2 1.219 0.173 MP = Matrix Polymer; SAP = Surface Active Polymer(25-50 wt % in PGMEA; mass values are based on polymer only); AP =Additive Polymer; A1 = camphorsulfonic acid; PAG =(4-(2-(tert-butoxy)-2-oxoethoxy)phenyl)diphenylsulfonium1,1,2,2,3,3,4,4,4-nonafluorobutane-1-sulfonate; 4M2P =4-Methyl-2-Pentanol; DPM = Dipropylene Glycol Methyl Ether; IBIB =Isobutyl Isobutyrate; PGMEA = Propylene Glycol Monomethyl Ether Acetate;and RCA = Receding Contact Angle. RCA value units are degrees (°). Allother value units are in grams (g).

Contact Angle Measurement

On a TEL ACT-8 wafer track, 8-inch silicon wafers were primed withhexamethyldisilazane (HMDS) at 120° C. for 30 seconds, coated with 385 Åof a respective topcoat composition and softbaked at 90° C. for 60seconds. The receding contact angle (RCA) for each of the topcoatcompositions was measured on a Kruss contact angle goniometer usingdeionized Millipore filtered water. Dynamic contact angle measurementswere carried out with 50 μL drop size and a tilt speed of 1 unit/sec.RCA was measured at the beginning of lateral drop motion before rapidacceleration. The results are shown in Table 4. The data in Table 2 showthat topcoat receding contact angle (RCA) above 81 degrees were achievedwith the topcoat compositions of the invention.

Immersion Lithography

Twelve-inch silicon wafers were spin-coated with AR™26N antireflectant(Rohm and Haas Electronic Materials) to form a first bottomantireflective coating (BARC) on a TEL CLEAN TRAC LITHIUSi+coater/developer. The wafers were baked for 60 seconds at 205° C.,yielding a first BARC film thickness of 760 Å. A second BARC layer wasformed over the first BARC by spin-coating AR™137 antireflectant (Rohmand Haas Electronic Materials), followed by baking at 205° C. for 60seconds to generate a 200 Å top BARC layer. EPIC™ 2096 positivephotoresist (Rohm and Haas Electronic Materials) was coated on the dualBARC-coated wafers and soft-baked at 120° C. for 60 seconds on a TELCLEAN TRACK LITHIUS i+coater/developer to provide a resist layerthickness of 1100 Å. Topcoat compositions of the examples were coatedover the photoresist layer and soft-baked at 90° C. for 60 seconds on aTEL CLEAN TRACK LITHIUS i+coater/developer to provide an overcoatthickness of 385 Å. The wafers were exposed through a mask on an ASMLTWINSCAN XT: 1900i immersion scanner using dipole (35-Y) illuminationwith 1.35 NA, 0.96 outer sigma, 0.76 inner sigma, X polarization and 42nm 1:1 line space patterns. The exposed wafers were post-exposure bakedat 90° C. for 60 seconds and developed with TMAH developer (2.38%) on aTEL CLEAN TRACK™ LITHIUS™ i+coater/developer to form resist patterns.

What is claimed is:
 1. A photoresist topcoat composition, comprising: afirst polymer comprising a first repeat unit of general formula (I) anda second repeat unit of general formula (II):

wherein: R₁ independently represents H, F or optionally fluorinated C1to C4 alkyl; R₂ represents optionally fluorinated linear, branched orcyclic C1 to C20 alkyl; L₁ represents a single bond or a multivalentlinking group; and n is an integer of from 1 to 5; a second polymercomprising a first repeat unit of general formula (III) and a secondrepeat unit of general formula (IV):

wherein: R₃ independently represents H, F or optionally fluorinated C1to C4 alkyl; R₄ represents linear, branched or cyclic C1 to C20 alkyl;R₅ represents linear, branched or cyclic C1 to C20 fluoroalkyl; L₂represents a single bond or a multivalent linking group; and n is aninteger of from 1 to 5; and a solvent.
 2. The photoresist topcoatcomposition of claim 1, wherein the first polymer is free of carboxylicacid groups.
 3. The photoresist topcoat composition of claim 1, whereinL₂ represents —C(O)OCH2-.
 4. The photoresist topcoat composition ofclaim 1, further comprising a third polymer comprising a first repeatunit of the general formula (II).
 5. The photoresist topcoat compositionof claim 4, wherein the third polymer further comprises a second repeatunit of general formula (V) and a third repeat unit of general formula(VI):

wherein: R₆ independently represents H, F, and optionally fluorinated C1to C4 alkyl; R₇ represents linear, branched or cyclic C1 to C20 alkyl;and R₈ represents a linear, branched or cyclic C1 to C20 fluoroalkyl. 6.The photoresist topcoat composition of claim 1, wherein the compositioncomprises a solvent mixture.
 7. The photoresist topcoat composition ofclaim 6, wherein the solvent mixture comprises: a first organic solventchosen from C4 to C10 monovalent alcohols; and a second organic solventrepresented by general formula (VII):

wherein: R₁₆ and R₁₇ are independently chosen from C3 to C8 alkyl; andthe total number of carbon atoms in R₁₆ and R₁₇ taken together isgreater than
 6. 8. A coated substrate, comprising: a photoresist layeron a substrate; and a topcoat layer formed from a photoresist topcoatcomposition of claim 1 on the photoresist layer.
 9. A method ofprocessing a photoresist composition, comprising: (a) applying aphotoresist composition over a substrate to form a photoresist layer;(b) applying over the photoresist layer a photoresist topcoatcomposition of claim 1 to form a topcoat layer; (c) exposing the topcoatlayer and the photoresist layer to activating radiation; and (d)contacting the exposed topcoat layer and photoresist layer with adeveloper to form a resist pattern.
 10. The method of claim 9, whereinthe topcoat layer is formed by spin-coating, and the first polymermigrates to an upper surface of the topcoat layer during thespin-coating, wherein an upper surface of the topcoat layer consistsessentially of the first polymer.